POSSIBLE INOP. TORQUE CONV. OR RELATED CONDITION

Model and Year: 1985-87 PASSENGER CARS AND TRUCKS WITH THM 440T4 OR 700R4 TRANSMISSIONS

TO: ALL CHEVROLET DEALERS

Information is provided in this bulletin for evaluation of the 245mm Torque Converter, diagnosis and possible Torque Converter failure used in THM 440-T4/HYDRA-MATIC 4T60 transaxles and THM 700-R4/HYDRA-MATIC 4L60 Transmissions.

CAUSES FOR A POSSIBLE TORQUE CONVERTER CONDITION ARE AS FOLLOWS:

- A broken dampener plate rivet (inside the converter).

These rivets hold the dampener assembly and the torque converter clutch apply plate together.

- Broken or loose spring tips.

The springs are used on the dampener assembly to aid in torsional shock during TCC apply and reducing converter clutch apply feel.

- Converter pump vanes broken or loose.

- Hydraulic leak due to worn or damaged seals.

- Delamination of converter clutch apply plate fiber material.

THE FOLLOWING IS A LIST OF SYMPTOMS THAT A VEHICLE MAY EXHIBIT UPON OR DURING TORQUE CONVERTER OPERATION:

- Shudder and/or Vibration during Torque Converter Clutch Apply.

- No Upshift due to fiber material sticking valves and/or fiber material and metal particles in filter.

- No Drive and/or Reverse.

- Converter sprag inoperative (no torque multiplication).

- Noisy converter bearings or excessive end play.

- Pinging noise (constantly).

- Vibration, out of balance, loose vanes (Noisy).

- Vehicle may exhibit Shudder or no TCC apply.

Torque Converter Clutch lining delaminating due to coolant contamination from transmission cooler.

- Torque Converter Clutch crowd shudder condition.

This condition is caused by a leak in the TCC circuit which could cause increased slippage and wear away the fiber lining on the TCC apply plate. Possible causes for TCC circuit leakage include: worn turbine shaft seals, TCC solenoid O-ring, valve body gaskets and auxiliary valve body gaskets, worn TCC accumulator piston pin or seal.

- TCC apply shudder caused by converter dampener plate not paraliel.

- A Whine noise when shifted into drive that may increase when brake torqued.

Torque converter Whine is usually noticed when the vehicle is stopped and when the transmission is in drive or reverse. The noise will increase when engine RPM is increased. The noise will stop when the vehicle is moving and there is no torque multiplication (both halves of the torque converter are turning at the same speed) or when the torque converter clutch is applied.

With foot on brake and Gear Selector in Drive, Depress accelerator to approximately 1200 RPM for no more than 6 Seconds (Stall Test). A Torque Converter Noise increases under load.

IMPORTANT: This noise should not be confused with pump whine noise which is usually noticeable in park, neutral and all other gear ranges. Pump whine will vary with pressure ranges.

- Chain and sprocket noise will be evident in park or neutral, and engine running. It is a whine or growl that increases and fades with vehicle speed, most noticeable under light throttle acceleration. A slipping chain will cause a loud rattle during heavy acceleration. Chain noise will stop when the transaxle is shifted into Drive or Reverse gear ranges with vehicle standing with foot on brake.

SERVICE NOTES:

THE CONVERTER SHOULD NOT BE REPLACED IF:

Fluid has an odor or is discolored but no evidence of metal or burned and distressed clutch plate material.

If the transmission condition did not display evidence of damaged or worn internal parts, steel particies or clutch plate lining material in unit and inside fluid filter.

Vehicle has been exposed to high mileage (only). The exception may be where the Torque Converter Clutch dampener plate lining has been exposed to excess wear by vehicles operated in heavy and/or constant traffic, such as taxi, delivery or police use.

THE TORQUE CONVERTER SHOULD BE REPLACED UNDER ANY OF THE FOLLOWING CONDITIONS:

Vehicle has TCC shudder and/or No TCC apply but, only after all Electrical and Hydraulic diagnosis has been made (Converter Clutch material may be glazed). Evidence of damage to the pump assembly or steel particles in converter. Steel particles are found after flushing the cooler and cooler lines.

External leaks in the hub weld area.

Converter pilot is broken, damaged or poor fit into crankshaft.

Converter hub is scored or damaged.

Internal failure to stator roller clutch.

Contamination from engine coolant.

Excess end play found after checking converter for end play.

Steel particles or clutch lining material found in fluid filter or on magnet when no internal parts in unit are worn or damaged indicating lining material came from converter.

Heavy clutch debris due to overheating (Blue Converter).

SERVICE MANUAL REFERENCE:

Refer to the Unit Repair section of your Service Manual whenever checking the torque converter for end play and/or replacement of the Torque Converter is necessary.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.